SINGAPORE - Unlike their counterparts in the land division, the police's Public Transport Security Command (TransCom) had no maps to refer to when navigating transport nodes a decade ago.

Instead, the team had to map out every single passageway in all the train stations and note down where each closed-circuit television camera was located.

The specialised unit under the Singapore Police Force (SPF) first started operations in 2009 and marks its 10th anniversary this year.

It was set up following the 2005 terror attacks on London's public transport system, when the authorities decided that a dedicated unit was needed to understand and navigate the complex underground terrain, recalled Mr Andy Tan, 49, who was commander of the unit from 2009 to 2011.

"When we started, we didn't even have directories of how the different MRT stations link together with the malls," said Mr Tan in a media interview on Tuesday (Nov 26).

"Can you imagine trying to pursue criminals, but nobody knows which way is (right)?"

Besides mapping out its terrain, TransCom also evolved from a counter-terrorism focus to preventing and combating crimes committed on public transport, said Mr Tan, who now works in another department in SPF.

A particularly memorable case in Mr Tan's time as TransCom commander was one in 2010 where vandals cut through SMRT's Changi depot fence and spray-painted graffiti on a train.

His team reviewed security footage at the depot, and the two vandals were identified.

The current TransCom team, which comprises mainly full-time national servicemen, has been trained to respond to common crimes on public transport, which include molestation, up-skirting and theft, said its current commander of TransCom, Assistant Commissioner Koh Wei Keong.

Officers also engage the community to help in operations through initiatives like Riders-on-Watch, he said.

The scheme has seen some 26,000 volunteers recruited since its launch in July. They are alerted to keep a lookout for persons of interest or someone who needs help through text messages from the police about such incidents.

"With a dwindling pool of NSmen, we need the community's help all the more in the years to come," said AC Koh.

Volunteers may be asked to take on bigger roles in the future, such as making joint patrols with TransCom officers, or acting as "contingency responders" to help officers in situations such as mass evacuations when "the more hands we have, the better it is", said AC Koh.